A user stated "I use Ubuntu 12.04 LTS and the gnome 3 shell ", what would be the correct tag to use? As I read it *gnome refers to the Standard Ubuntu
By default, Ubuntu uses Unity instead of GNOME Shell. Both are GNOME. The GNOME Shell is the official shell for GNOME--Unity is Ubuntu's alternative shell.
For that reason, it would be misleading to use gnome to refer to an Ubuntu desktop with Unity, without also using it to refer to an Ubuntu desktop with GNOME Shell. GNOME Shell is officially part of GNOME. As far as the GNOME project is concerned, Unity is an unofficial replacement part for GNOME Shell.